562 



TABLES 602-609.— PHOTOGRAPHY * 



TABLE 602.— SENSITOMETRIC CONSTANTS OF TYPE PLATES AND FILMS, 



DEFINITIONS 



Density (D).— Density is a measure of the degree of blackening of an exposed film or 

 plate after development. Density is defined in general terms as the logarithm of the ratio 

 of the radiant flux, P , incident on the sample to the radiant flux, P%, transmitted by the 

 sample. 



3.0 



2.0 



1.0- 



i.O 



Log exposure (mcs) 



Fig. 27. — Typical characteristic curve. Ordinates are diffuse transmission density (D) ; 

 abscissae, logs of exposure (log E). A-C = toe, C-E = straight line, E-F = shoulder, 

 B = speed point, B-D = Alog E = 1.50. Tan = 7, Tan b = /9, Tan a = 0.3/3. 



D 



=*(*) 



Exposure (E). — E = It (expressed in meter-candle seconds). / = illumination (meter- 

 candles, mc) incident on the photographic material during exposure, t = exposure time in 

 seconds. 



Gamma (7). — Gamma is defined as the tangent of the angle alpha (a) (fig. 27) which 

 the straight-line part of the characteristic curve makes with the log-exposure axis. 



Gamma infinity (700 ). — 700 is defined as the limiting value to which gamma ap- 

 proaches as development time is increased. 



Time of development for the half gamma infinity (t y = y x /2). — A convenient 

 practical specification of development rate of significance in comparing developers. 



Time of development for gamma of unity (t y = 1.0).— A convenient practical speci- 

 fication of development rate of significance in comparing photographic materials. Compari- 

 sons must be confined to materials in the same developer. 



Inertia (»). — t = the value of exposure where the straight-line portion of the character- 

 istic curve (fig. 27) extended cuts the log E axis. 



Speed (S c ).—Se = l/E, where E is the exposure corresponding to point B on the 

 D-log E curve in figure 27. This point is located in the following manner : A log exposure 

 range of 1.50, represented in the figure by the distance along the log exposure axis between 

 B and D, is selected in a region where the slope of the curve at the low end of the range is 

 0.30 of the average slope over the entire range. When the slope, or tangent of angle a, is 

 0.30 of the tangent of angle b, the point B, at the low end of the exposure range, represents 

 the exposure value (E) from which the speed of the material is derived. 



* The material on photography was prepared by L. A. Jones, of the Eastman Kodak Co. 



SMITHSONIAN PHYSICAL TABLES 



